System and Method for Controlling Temperature in a Forehearth

ABSTRACT

Systems and methods are provided for controlling temperature in a glass forehearth. In one implementation, a system includes at least one burner disposed in said forehearth, a manifold coupled to said burner, a combustion fuel supply coupled to said burner, a combustion air blower for delivering ambient air under pressure to said manifold, and a controller coupled to said burner for controlling operation of said burner. The system may include a temperature sensor operatively coupled downstream of the blower for providing to the controller a temperature signal indicative of temperature of air delivered to the manifold by the blower. The controller may be responsive to the temperature signal for controlling operation of the burner as a function of current temperature of air fed to the manifold. Operation of the burner may also be controlled as a function of an average air temperature over a preceding time duration.

This application is a division of application Ser. No. 12/434,354 filedMay 1, 2009.

The present disclosure relates generally to glassware forming and moreparticularly to systems and method for controlling temperature in aforehearth.

BACKGROUND AND SUMMARY OF THE DISCLOSURE

In glassware manufacture, it is known to provide a glass forehearth thetemperature of which is maintained by one or more combustion burners.Operation of the burners may be controlled as a function of feedbackobtained from thermocouples disposed in contact with the molten glass inthe sidewall channels of one or more zones of the forehearth.Accordingly, detected changes in the temperature of the glass as sensedby the in-glass thermocouples may be used to vary the output of theburners as desired to achieve a desired glass temperature in a givenzone of the forehearth. While this may be a generally accurate way toadjust forehearth zone temperatures, the in-glass thermocouples areexpensive and require higher capital investments for a given forehearth.

The present disclosure embodies a number of aspects that can beimplemented separately from or in combination with each other.

In one implementation, a system is provided for controlling temperaturein a forehearth that includes at least one burner disposed in theforehearth for heating glass in the forehearth, a manifold coupled tothe burner, a combustion fuel supply coupled to the burner, a combustionair blower for delivering ambient air under pressure to the manifold,and a controller coupled to the burner for controlling operation of theburner. The system may include a temperature sensor operatively coupleddownstream of the blower for providing to the controller a signalindicative of temperature of air delivered to the manifold by theblower. The controller may be responsive to this temperature signal forcontrolling operation of the burner as a function of current temperatureof air fed to the manifold. The controller may also control operation ofthe burner as a function of an average air temperature over a precedingtime duration. In one form, the average air temperature is a movingaverage air temperature over a predetermined time period.

According to at least one implementation, a method is provided forcontrolling glass temperature in a forehearth that includes at least oneburner associated with the forehearth for heating glass in theforehearth, a manifold coupled to the burner, a combustion fuel supplycoupled to the burner, and a combustion air blower for deliveringambient air under pressure to the manifold. The method may includeproviding to the controller a signal indicative of the combustion airpressure provided to the burner, providing to the controller a signalindicative of the temperature of air downstream of the blower, andcontrolling the output of the burner as a function of these pressure andtemperature signals. In at least one form, the mass flow rate of acombustible air/fuel mixture is maintained constant over varyingcombustion air temperatures to at least reduce the effect of, forexample, changing ambient air temperature.

According to at least one implementation a method is provided forcontrolling glass temperature in a forehearth that includes at least oneburner associated with the forehearth for heating glass in theforehearth, a manifold coupled to the burner, a combustion fuel supplycoupled to the burner, a combustion air blower for delivering air underpressure to the manifold, and a cooling air supply communicated with themanifold. The method may include generating a nominal burner pressurecurve as a function of the amount of cooling air provided to themanifold wherein the pressure curve includes a first portion in whichthe temperature downstream of the burner over a first range of desiredtemperature conditions is controlled at least primarily by adjusting theamount of cooling air provided to the system and the pressure curveincludes a second portion in which the temperature downstream of theburner over a second range of desired temperature conditions differentfrom the first range is controlled at least primarily by adjusting theburner pressure. The method may also include controlling the burnerpressure as a function of the nominal burner pressure curve. In oneform, the burner pressure is controlled as a function of the current airtemperature downstream of the blower and also may be controlled as afunction of an average air temperature downstream of the blower over apreceding time period.

BRIEF DESCRIPTION OF THE DRAWINGS

The disclosure, together with additional objects, features, advantagesand aspects thereof, will best be understood from the followingdescription, the appended claims and the accompanying drawings, inwhich:

FIG. 1 is a diagrammatic view of a portion of a glass forming systemincluding a forehearth;

FIG. 2 is a graph of glass temperature in different forehearth zones asa function of ambient air temperature without compensation for changesin ambient air temperature;

FIG. 3 is a graph of glass temperature in different forehearth zones asa function of ambient air temperature with compensation for ambient airtemperature changes;

FIG. 4 is a schematic diagram of a control system for a glass forehearthincluding combustion burner pressure control as a function of input airtemperature;

FIG. 5 is a schematic diagram of a forehearth control system includingcombustion burner pressure control as a function of input airtemperature and based on a predetermined heat cool curve; and

FIG. 6 is a representative heat-cool curve such as may be used in thecontrol system of FIG. 5.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Referring in more detail to the drawings, FIG. 1 illustrates a portionof a glassware forming system 10 including a glass forehearth 11 throughwhich molten glass flows during the production of glassware. Theforehearth 11 may include back, middle and front zones 12, 14, 16 eachof which may include one or more thermocouples 18 for feedback controlo£ for example, the temperature within the various zones 12, 14, 16. Afan or combustion air blower 20 provides a forced current of ambient airunder pressure to a main header or manifold 22 that routes the air tothe various zones 12, 14, 16 which each may include, receive therein, orotherwise be associated with, one or more combustion burners 24. Themanifold 22 distributes to the combustion burners 24 a combustiblemixture of fuel from a fuel supply 26 and air from the combustion blower20. The flow rate through a given combustion burner 24 may be controlledby a valve 28, the position or open extent of which may be set andcontrolled by a suitable controller 30. The controller 30 may alsocontrol the operation of the blower 20, flow rate from the fuel supply26 to the manifold (such as via a valve 32), the flow rate of a coolingair supply 31 to the forehearth zones 12, 14, 16 (such as by controllingone or more supply valves 33) and many other functions within theglassware forming system 10. Of course, multiple controllers could beprovided with each handling certain tasks, as desired, and the fuelsupply 26 may be coupled to the burners either through the manifold 22,or downstream of the manifold 22.

In use, as the temperature of air fed to the combustion burners 24changes, so does the density of the air flowing through the combustionburners 24. Accordingly, the mass flow rate of gas and air that flowsthrough the combustion burners 24 can vary for a given position of itsvalve 28 as the air temperature varies. In this manner, the output of acombustion burner 24 can vary over a given set point of its controlvalve (i.e. a given position of the valve), and hence, the temperaturewithin the forehearth zones can likewise change.

Also, the output pressure of the combustion blower 20 varies as afunction of the volume of air the system draws from the blower and bythe ambient temperature of the air supplied to the blower 20. In asystem with automatic temperature control, such as feedback controlbased on glass temperature, there will be a varying volume demand fromthe combustion blower 20 which creates a variation in its supplypressure. Because a single blower 20 may provide air to more than one,or even all, of the combustion zones 12, 14, 16 on a single forehearth11, changes in the volume requirements of any single zone 12, 14, 16within the forehearth 11 can interact and affect the supply pressure tothe other zones. Further, ambient air temperature at the inlet of theblower 20 has an inverse effect on the outlet pressure of the blower 20for a given power demand. This effect on the outlet pressure will affectall combustion zones 12, 14, 16 within the foreheath 11 concurrently andin the same general direction (that is, increasing or decreasingpressure). Accordingly, as the air temperature flowing through theblower 20 increases, the outlet supply pressure of the blower 20decreases, and vice versa.

Further, temperature changes in the ambient air supplied to the blower20 provide changes in the density of the air at the blower. And theblower 20 itself can heat the air with the amount of work or heatapplied to the air by the blower varying as a function of the demandfrom the system 10. In general, higher air demands from the blower 20mean that the air is resident at the blower for a shorter period of timeand hence is heated less by the blower whereas times of low demand bythe system 10 permit the air to be heated more by the blower 20.Accordingly, the ambient temperature change as well as the temperaturechange caused by the blower 20 can affect the output conditions of theblower 20 and the density of the air discharged from the blower to themanifold 22.

To accommodate for the changes in air conditions within the forehearthsystem 10, a control strategy may use feedback from one or more manifoldpressure sensors 34, and a temperature sensor 36 to enable control ofthe combustion burners 24. The manifold pressure sensor 34 may becoupled to the manifold and operable to send a signal to the controllerthat is indicative of the pressure within the manifold 22. Thetemperature sensor 36 preferably is operatively coupled downstream ofthe blower 20 so that it is responsive to not only ambient airtemperature changes, but also the changes in air temperature caused bythe blower itself. Accordingly, the temperature feedback can be used tovary the flow rate through the combustion burner valves 28 as a functionof the temperature and density changes in the air delivered to thecombustion burner valves. In one implementation, the combustion burners24 may be controlled to provide a generally constant mass flow rate ofthe gas and air combustion mixture to each zone 12, 14, 16 of theforehearth 11. In one exemplary implementation, operating a forehearthusing the temperature compensated generally constant mass flow ratecontrol to each forehearth combustion zone reduced ambient temperatureeffects by about 75 percent. In addition to or instead of controllingthe open extent of the burner valves 28, the blower 20 could have avariable output that may be modified by the controller to control theflow rate through the burner valves 28 and/or combustion burners 24.

The temperature compensated mass flow rate control can be implemented byaugmenting operation of the combustion burner valves 28 with acompensation factor 38 (FIGS. 4 and 5) derived as a function of thetemperature feedback provided from the temperature sensor 36 (FIG. 1).In this way, the combustion burner valve set point (that is, the extentto which the valve 28 is open) is modified by the controller 30 inresponse to the temperature feedback data. This is shown schematicallyin FIG. 4 wherein a nominal combustion burner valve control value 40 andtemperature data 42 from the temperature sensor 36 are inputs to thecontroller 30 (FIG. 1) and the controller 30 provides an outputcombustion burner control value 44 that may, depending on thetemperature sensor data, differ from the nominal value by a temperaturecompensation factor 38.

In one implementation, the temperature compensation factor 38 is derivedas a function of the differential pressure across the combustion burnervalve 28. This assumes, more or less, that the discharge pressure of theburner 24, which is equal to the internal pressure in the forehearth 11,is very low compared to the upstream pressure in the manifold 22 leadingto the combustion burner 24. Given these assumptions, the temperaturecorrected mass flow across the combustion burner valves 28 can beexpressed as:

$Q = {K\sqrt{h*\frac{Td}{Tf}}}$

where Q equals mass flow, K is a flow calibration constant, h is thedifferential pressure across the combustion burners, Td is the designtemperature (absolute units), and Tf is thesensed temperature (absolute units). From this, the burner pressurerequired for a specific mass flow is given by the equation:

$h = {\left( {Q/K} \right)^{2}*\frac{Tf}{Td}}$

Since the mass flow rate, Q, is held to a constant value, the square ofone constant divided by another constant can be expressed as a thirdconstant, K₂, or:

$h = {K_{2}*\frac{Tf}{Td}}$

From this, the combustion burner valve operation can be adjusted asnecessary to achieve the desired combustion burner operating pressure toachieve the desired flow rate through the burner even as the airtemperature varies due to ambient temperature changes or changes causedby the blower 20.

Further, so that the system 10 can make smaller incremental correctionsover the day and night temperature swings that are corrected orcompensated to the seasonal average temperature, the presently sensedair temperature can be compared to a moving average manifoldtemperature. The moving average temperature may include temperature dataacquired over some recent, pre-determined time period. In this manner,the combustion burner valve set point can be varied based on ambienttemperature as a function of a moving average temperature over a givenperiod of time. If the moving average temperature is examined over tooshort a period of time, for example less than about 2 days, thevariations of the moving average temperature may be too great. If themoving average is taken over too long of a time the temperaturevariations may not be great enough to provide the desired control. Inone presently preferred implementation, a moving average temperature ofbetween 5 to 15 days may be used, and one presently preferred formincludes the average temperature over the immediately preceding 10 days.This may be represented by the following formula:

$h_{TSP} = {\frac{Tf}{T_{movavg}}*h_{RSP}}$

where h_(TSP) equals manifold pressure “true set point” which is thecorrected combustion burner pressure required to maintain constant massflow rate; h_(RSP) equals manifold pressure “requested set point” whichis the combustion burner valve control data which would be used absentthe temperature compensation of this formula; Tf equals flowing airtemperature in the combustion manifold 22; and T_(movavg) equals themoving average of manifold air temperature.

The benefit of the temperature compensated mass flow rate control of thecombustion burner valves 28 can be seen by comparing FIG. 2 to FIG. 3.In these figures, ambient temperature is plotted as line 46 and glasstemperatures in two sections (e.g. left and right) of a forehearth zone12, 14, or 16 are plotted as lines 48 and 50. In these figures, anambient temperature drop of about 20° Fahrenheit occurred between about4 o'clock and 9 o'clock. In FIG. 2, which is a plot of empirical datafrom a forehearth system without ambient temperature compensation, theglass temperatures in the two forehearth sections increasedsignificantly during that time. In contrast, the forehearth system 10shown in FIG. 3 included ambient temperature control as set forth hereinand the glass temperatures in the forehearth sections remained nearlyconstant despite a similar ambient air temperature change. Thisdramatically improved control of the glass temperatures despitesignificant ambient temperature change, accounts for nearly all of therecorded changes in the glass temperatures within the forehearth. Otherfactors contribute to relatively minor changes in glass temperature andmay have other root causes.

Finally, to enable further automated control of the forehearth system 10with ambient temperature compensations, a graph or table can begenerated to control glass temperature or another temperature within orassociated with the forehearth. With this graph, the combustion burners24 are controlled based on the pressure within the manifold 22 (which isthe pressure provided to the combustion burners 24), so that, forexample, air density changes are accommodated. Individual pressuresensors at each burner could be provided in addition to or instead ofthe manifold pressure sensor 34, if desired. Nominal combustion burnerpressures over a wide range of temperature conditions can be set bytrial and error for any given system, with changes from that (e.g. dueto ambient temperature changes) made by the control strategy implementedin the controller 30.

A representative temperature control graph 51 including nominal burnerpressure curves 52, 54 is shown in FIG. 6. On this graph 51, the controldata or curves for two combustion burners 24 are shown. In this example,the combustion burner pressures remain generally constant over a firstportion of the graph, and the system temperature requirements are variedby adjusting the flow rate of cooling air input to the system, which isshown by curve 60. However, at some point reducing the cooling air flowby increasingly closing the supply valves 33 may not be sufficient tomaintain or reach a desired temperature and the burner pressures must beincreased to increase the combustion burner output.

In the representative graph, the transition from temperature controlsolely or primarily by cooling air adjustments to temperature controlsolely or primarily by burner pressure adjustments occurs at about 90%of controller output. At 90% of controller output the cooling air supplyvalve(s) is about 90% closed (or at 90% of the extent to which it can beclosed by the controller). For a given operating condition, reducing thecooling air flow will increase the temperature in the correspondingportion of the forehearth for a given combustion burner output. In therepresentative system with which this control graph may be used, furtherreduction of the cooling air beyond 90% controller output valve is notsufficient to maintain or reach a desired temperature in the forehearth.Therefore, the pressure of the combustion burners is increased toincrease burner output and thereby increase the temperature in thecorresponding portion of the forehearth. In the example shown, thecombustion burner pressure is increased from about 2.5 in H₂0 up toabout 6 in H₂0 at maximum system output level, although other values andrates of change of burner pressures can be used. Also in the exampleshown, when the burner pressures are adjusted the cooling air ismaintained at or near a constant, minimum value of about 5 to 10% ofmaximum closure of its control valve to the maximum system output level.In typical operation, the system 10 will require something greater thanthe minimum operating level (0% controller output, maximum cooling airflow) and less than the maximum operating level (100% controller output,minimum cooling air flow, maximum burner pressure). In one exemplarysituation, as shown by the dashed line 62, the system is operating atabout 47% of controller output at which the cooling air supply valve(s)is at about 48% open, a first combustion burner pressure (shown in line52) is about 2.8 in H₂0 and the second combustion burner pressure (shownin line 54) is about 2.5 in H₂0.

As shown by FIG. 5, the burner pressure curves or values taken from thegraph 51 of FIG. 6 are nominal values used as an input in the controlstrategy providing for ambient temperature correction. In use, theburner pressure values taken from the graph of FIG. 6 (or other suitablesource like a look-up table or other data collection) may be adjusted bythe temperature compensation factor 38 discussed above to provide aconstant mass flow rate adjusted for ambient temperature changes as afunction of an average temperature over a desired time period (e.g. the10-day moving average temperature discussed above).

The combustion burner pressure can be varied as desired over the firstportion of the graph 51 (that is, when cooling air flow adjustment issolely or primarily utilized for temperature control) and need not bemaintained constant as shown in the example. In at least someembodiments, the rate of change of the combustion burner pressure may beless than the rate of change of the cooling air over the first portionof the graph 51 which corresponds to a first range of forehearthoperating conditions. The cooling air flow could likewise be varied inthe second portion of the graph 51 (that is, when combustion burneradjustment is solely or primarily utilized for temperature control)rather than holding its valve at or near a constant position. In atleast some embodiments, the rate of change of the cooling air may beless than the rate of change of the combustion burner pressure over thesecond portion of the graph 51 which corresponds to a second range oftemperature conditions. Further, the point at which burner pressureadjustment is used to solely or primarily control temperature could beanywhere along the graph as desired, and the burner pressures may beincreased while the cooling air flow still is being decreased, or beforethe final decrease in the cooling air flow, as desired.

The disclosure has been presented in conjunction with several exemplaryembodiments, and additional modifications and variations have beendiscussed. Other modifications and variations readily will suggestthemselves to persons of ordinary skill in the art in view of theforegoing description. For example, without limitations, the systems andmethods may be utilized with different forehearth configurations,including configurations wherein a separate blower is used for eachforehearth zone, the combustible fuel supply is provided downstream ofthe main header or manifold, and other configurations, as desired. Thedisclosure is intended to embrace all such modifications and variationsas fall within the spirit and broad scope of the appended claims.

1. A method for controlling glass temperature in a forehearth thatincludes at least one burner associated with said forehearth for heatingglass in said forehearth, a manifold coupled to said burner, acombustion fuel supply coupled to said burner, a combustion air blowerfor delivering air under pressure to said manifold, and a cooling airsupply communicated with the manifold, said method including: generatinga nominal burner pressure curve as a function of the amount of coolingair provided to the manifold wherein the pressure curve includes a firstportion in which the glass temperature downstream of the burner over afirst range of desired temperature conditions is controlled at least inpart by adjusting the amount of cooling air provided to the system andthe pressure curve includes a second portion in which the temperaturedownstream of the burner over a second range of desired temperatureconditions different from the first range is controlled at leastprimarily by adjusting the burner pressure; and controlling the burnerpressure as a function of the nominal burner pressure curve.
 2. Themethod set forth in claim 1 wherein during said second portion of thepressure curve the rate of change of the cooling air is less than therate of change of the burner pressure.
 3. The method set forth in claim2 wherein the cooling air is maintained constant during said secondportion of the pressure curve.
 4. The method set forth in claim 1wherein during said first portion of the pressure curve the rate ofchange of the burner pressure is less than the rate of change of thecooling air.
 5. The method set forth in claim 1 wherein the burnerpressure is maintained constant during said first portion of thepressure curve.
 6. A method for controlling glass temperature in aforehearth that includes at least one burner associated with saidforehearth for heating glass in said forehearth, a manifold coupled tosaid burner, a combustion fuel supply coupled to said burner, and acombustion air blower for delivering ambient air under pressure to saidmanifold, said method including: providing to said controller a signalindicative of the combustion air pressure provided to said burner;providing to said controller a signal indicative of the temperature ofcombustion air downstream of said blower and delivered to said manifold;and controlling the output of said burner as a function of the pressureand temperature signals.
 7. The method set forth in claim 6 wherein themass flow rate through said burner is controlled by said controller as afunction of the temperature and pressure signals.
 8. The method setforth in claim 6 wherein the output of said burner is controlled also asa function of an average combustion air temperature over a precedingtime duration.
 9. The method set forth in claim 8 wherein said averageair temperature is a moving average combustion air temperature over apreselected preceding time duration.
 10. The method set forth in claim 9wherein said moving average combustion air temperature is over apreceding time duration of at least two days.
 11. The method set forthin claim 8 wherein said moving average combustion air temperature isover a preceding time duration of between 5 and 15 days.